The subpixel rendering is a technique for displaying an image with a resolution higher than the original resolution of a display device, such as OLED (organic light emitting diode) display panels and LCD (liquid crystal display) panels, by performing image data processing on image data of the original image. In the following, image data process for achieving subpixel rendering may be referred to as subpixel rendering process. A subpixel rendering process involves generating image data used for driving M pixels of a display device from image data associated with N pixels of the original image, where N and M are natural numbers satisfying N>M.
A subpixel rendering process is achieved in light of gamma characteristics of the display device. Discussed below is the case where image data used for driving one pixel of a display device is generated from image data associated with two pixels of the original image through a subpixel rendering process, while the grayscale value of each subpixel is represented by eight bits in the image data of the original image and the image data used for driving each pixel of the display device. When the grayscale values of the R subpixels of first and second pixels are described as being “255” and “0”, respectively, in the image data of the original image, and the grayscale value of the R subpixel of the corresponding pixel of the display device is calculated by simply averaging the grayscale values of the R subpixels of first and second pixels in the subpixel rendering process, the result is a grayscale value of “127.5”. When the R subpixel of the corresponding pixel of the display device is driven with the grayscale value of “127.5”, the brightness of the R subpixel becomes 22% for a gamma value γ of 2.2. However, in one embodiment, the R subpixel of the corresponding pixel of the display device is driven so that the brightness of the R subpixel becomes 50%, since the grayscale value of “255” corresponds to the brightness of 100% and the grayscale value of “0” corresponds to the brightness of 0%. When the gamma value γ of the display device is 2.2, the grayscale value of the R subpixel of the corresponding pixel of the display device is calculated as “186” in the subpixel rendering process.
Accordingly, a subpixel rendering process generally includes performing gamma conversion on the grayscale values described in image data of the original image (that is, calculating the γ powers of the grayscale values of the image data), calculating image data associated with M pixels of the display device on the basis of the image data obtained by the gamma conversion, and then performing inverse gamma conversion (that is, calculating the 1/γ powers of the grayscale values of the image data).
Such subpixel rendering process may cause an increase in the circuit size. The gamma conversion and the inverse gamma conversion involve calculation of a power. As widely known to persons skilled in the art, a circuit performing calculation of a power has a large circuit size. For example, to perform a gamma conversion or an inverse gamma conversion is to use an LUT (lookup table); however, use of an LUT to achieve gamma conversion or inverse gamma conversion increases the circuit size.
Thus, there is a technical need of reducing the circuit size of a circuit which performs a subpixel rendering process.